It is previously known to clean hydraulic liquid in industrial trucks.
Hydraulic systems in general, have an incorporated filter which is positioned at the return flow to a container for the hydraulic liquid, generally named the hydraulic reservoir. This filter is of low pressure type. The filter cleans the liquid by means of the return flow to the hydraulic reservoir. In JP 6081815 A, such a hydraulic circuit is disclosed, in which the idea of cleaning with a low pressure filter at the hydraulic reservoir has been further developed. JP 6081815 A discloses a hydraulic circuit with a pump, two hydraulic pistons, the hydraulic circuit presents further two direction change valves which are maneuvered by two magnetic valves. The hydraulic circuit comprises a return pipe that conducts hydraulic liquid back to the hydraulic reservoir on the return pipe is positioned a return filter. The circuit includes a main pump and a control pump. In the circuit of the control pump is installed a filter on the pressure side, to increase the cleaning and for example lower the wear of the valves. By this it has been solved the problem of lowering the wear of the valves and achieves an increased cleaning, at the same time as the filter does not clog in the same manner as if the filter had been coupled on the main circuit.
The know (prior) art for improved cleaning of hydraulic circuits, in addition to what is provided by the return filter, is in other words built on introducing a high pressure filter on the pressure side of the pump. These filters provide problems with pressure losses from the pump, and result in increased costs for the hydraulic circuit. To introduce a high pressure filter on the pressure side after the pump also confers spacing problems.
The solution to at least one of these problems is presented below.